The present invention relates to an electromagnetic induction means having a condensable cooling liquid as a cooling medium. Hereinafter, an explanation will be given in respect of the use of a transformer as such an electromagnetic induction means.
In a transformer of this kind, heated elements such as the iron core, the windings or the like are immersed in a cooling medium so that the heated elements are cooled with the evaporative latent heat of the cooling medium. Hence, the cooling efficiency is high. Furthermore, since mineral oil is not used, the device is non-combustible and non-explosive, the size thereof is small and the weight thereof is light. Thus, a transformer of this kind has many good characteristics, and recently, much attention has been focused thereon.
In the past, there has been known a transformer of this kind as shown in FIG. 1. In FIG. 1, reference numeral 1 denotes an iron core and reference numeral 2 denotes windings which are wound around the iron core 1 and which are composed of a primary winding 2a and a secondary winding 2b. Reference numeral 3 denotes a duct I between the iron core 1 and the secondary winding 2b, and reference numeral 4 denotes a duct II between the primary winding 2a and the secondary winding 2b.
The inner members of the transformer constituted as described above are stored in a tank 5. A cover 6 is mounted on the upper end of the tank 5 so that the inner members of the transformer are tightly covered by the tank 5 and the cover 6.
There are mounted a primary terminal 7 and a secondary terminal 8 on the side surfaces of the tank 5. Lead wires 9a, 9b, which are drawn out from the primary winding 2a and the secondary winding 2b, respectively, are connected thereto. There is provided a cooling means 10 on the cover 6.
A condensable cooling liquid 11 is enclosed in the tank 5. A condensable vapour 12 in the gaseous phase which is caused as the result of the evaporation of the cooling liquid 11 appears in the upper space in the tank 5 and the inner spaces of the cooling means 10.
If the transformer constituted as described above is driven, the windings 2 and the iron core 1 become heating elements, so as to raise the temperature thereof. If the temperature of the windings 2 and the iron core 1 become high, the condensable cooling means 11 is heated so as to evaporate and remove the evaporative latent heat from the windings 2 and the iron core 1, thereby cooling the same. The condensable vapour 12 caused as the result of condensable cooling medium evaporation as mentioned above fills in the upper space of the tank 5 and the inner spaces of the cooling means 10 and is cooled by the cooling means 10, so that the evaporative latent heat is removed from the transformer to result in liquid. The condensable cooling liquid 11, which has thus again become liquid, forms drops which fall downwardly under their own weight.
Since the condensable cooling liquid 11 is enclosed in the tank 5 in a manner such that the elements of the iron core 1 and the windings 2 are immersed therein in accordance with the prior art as mentioned above, the quantity of evaporative cooling liquid 11 is determined by the volume of the tank 5 and the volumes of the windings 2 and the iron core 1. However, the minimum quantity of cooling liquid 11 necessary for cooling the heated elements of the windings 2 and the iron core 1 is determined mainly by the quantity of heat generated by these elements and the quantity of evaporative latent heat of the condensable cooling liquid 11. The minimum quantity of condensable cooling liquid obtained thereby is much smaller than the quantity of the liquid normally enclosed in the tank 5. The price of C.sub.8 F.sub.16 O or the like which is commonly used as the condensable cooling liquid 11 is high, generally several times to about ten times the price of the insulating material which forms the inner members of the transformer. Therefore, the quantity of condensable cooling liquid 11 used was much more than the minimum quantity required for cooling in accordance with the prior art. Hence, there exists a drawback in that the price of the prior transformer is unnecessarily high.
U.S. Pat. No. 4,145,679 to Mitchell discloses an assembly which, as indicated at lines 44-51 includes an inert filler material in the form of a cellular foam or pressboard to minimize the amount of liquid dielectric required. However, the construction disclosed by Mitchell lacks simplicity in design and manufacture and does not allow for any spacing between the outer conductors and the filler if such is desired for cooling. In addition, the filler material in Mitchell must be inserted just prior to introducing the dielectric fluid and cannot be introduced earlier, or simultaneously with other, prior steps because of the effect thereon of subsequent vacuum heating treatments that may desirably be performed on the inductor core, windings and the tank.